The present invention relates to a card type semiconductor memory device and, more particularly, to a card type semiconductor memory device for storing a color interleaved analog image signal obtained using an image sensing element.
Generally, in an image sensing element for photographing a color still image, color filters of different colors (e.g., RGB: red, green, and blue) are arrayed in a Bayer matrix (substantially checkerboard pattern repeating array) in units of pixels, and an object luminance of a predetermined color is detected at each pixel position.
A still image formed from the luminance values of the pixels is output as a color interleaved analog image signal, i.e., a color interleaved analog image signal made of analog signals which have amplitudes representing the respective luminance values and are discrete on the time axis.
Conventionally, in, e.g., a digital still camera apparatus, a digital memory is used as a storage medium for storing a still image obtained with an image sensing element. After a color interleaved analog image signal is converted into digital data by an A/D converter, image data having color information (RGB data) of each pixel is prepared, compressed, and stored.
However, according to this method, a processing time of about 5 to 10 sec is required to store a still image with a resolution of 1,000,000 pixels or more. This apparatus cannot photograph images at a short interval.
Currently, for, e.g., a digital still camera apparatus, a method has been examined in which a color interleaved analog image signal with an analog value is stored at a high speed using an analog nonvolatile semiconductor memory as a medium for storing a still image.
Conventional storage media of this type store digital data. Card type semiconductor memory devices (e.g., smart media) detachable from a digital still camera apparatus are also used. A card type semiconductor memory device for storing an analog signal has also been examined.
However, when a card type semiconductor memory device is formed by simply containing a plurality of analog nonvolatile semiconductor memories in one card-like package, the number of connector signal lines necessary to externally output, from the card type semiconductor memory device, analog signals read out from the individual analog nonvolatile semiconductor memories increases. This impedes size and cost reduction of the card type semiconductor memory device.
In displaying a still image or in various image processing operations, RGB image data having luminance information of all of the RGB colors in units of pixels are generally used.
Conventionally, in, e.g., a digital still camera apparatus, a color interleaved analog image signal obtained using an image sensing element is converted to obtain color (RGB) image data. Even when an analog nonvolatile semiconductor memory is used, a color interleaved analog image signal read out from this memory must be converted into color image data.
To convert a color interleaved analog image signal into color image data, the luminance information of at least eight pixels positioned around a pixel to be processed is necessary.
Hence, the luminance information of a total of nine pixels need be read out from corresponding analog nonvolatile semiconductor memories. Especially when the analog signal is to be directly converted into color image data at a high speed, the pixel array must be parallelly read out.
Unlike digital signals, analog signals can hardly share one signal line because their transient characteristics have delays due to the capacitance component of a signal line and errors are generated in the amplitudes as the clock frequency becomes high. Hence, the number of connector signal lines increases to impede size reduction of a card type semiconductor memory device.
The present invention has been made to solve the above problems, and has as its object to provide a card type semiconductor memory device capable of writing or reading a still image at a high speed using a small number of connector signal lines.
In order to achieve the above object, according to the present invention, there is provided a card type semiconductor memory device, wherein at least one memory chip for storing a still image and connection means having a number of signal lines for transferring various signals between the memory chip and a host device are mounted on a card-like substrate, the memory chip comprising a memory section comprising analog nonvolatile semiconductor memories for sequentially storing, as analog values, color interleaved analog image signals having analog luminance information of predetermined colors in units of pixels in synchronism with a predetermined clock signal, and a signal processing section for calculating, as analog values, the luminance information at a plurality of pixel positions, which are read out from the memory section, to convert the luminance information into color image data having analog luminance information of the respective colors in units of pixels, and outputting the color image data.